Project 1 - Toxicity and Liver Carcinogenicity of 1,4-Dioxane: Single Chemical and Mixtures Studies

项目总结 1，4-二恶烷(1，4-DX)是一种新兴的饮用水污染物。接触1，4-DX的可能性是 适用于居住在Superfund或其他类型的1，4-DX投放点附近的人。国际环境保护署 癌症研究已将1，4-DX列为2B类致癌物质，其主要器官靶标是 动物研究中的肝脏。尽管存在这种担忧，但饮用水中1，4-DX的安全标准一直进展缓慢 发展和变化很大，变化与其肝脏相关的不确定性有关 致癌潜力。迫切需要机制研究来(I)了解1，4-DX可能起到的作用 单独或与其他共同存在的饮用水污染物[例如 三氯乙烯(TCE)和1，1-二氯乙烷(1，1-DCA)]，(Ii)确定暴露浓度范围 这些影响在其上发生，以及(Iii)识别潜在的更易受伤害的亚群。我们的初步研究 揭示了可能参与1，4-DX致癌的分子靶点和途径 这是进行拟议研究的阶段。这些初步研究使用了不同的1，4-DX浓度(50,500 和5,000 ppm)放入饮用水中，最长可达3个月。这些研究显示肝脏有轻微的细胞毒性。 这与之前的研究一致。1，4-DX的最大剂量可引起多种分子变化 肝脏包括：(I)持续诱导NRF2及其参与抗氧化反应的靶蛋白(即， GCLC、GCLM、Hmox1和NQO1)，(Ii)依赖时间诱导的CYP2E1(关键氧化途径 激活内源和外源化合物以及产生活性氧物种)，(Iii) 小叶中心积聚脂质过氧化副产物4-HNE，以及(Iv)DNA损伤升高 标记γH2 AX。重要的是，这些1，4-DX引起的分子变化在小鼠模型中被放大。 全身性谷胱甘肽缺乏症。这个项目将在这些有趣的发现的基础上，调查我们的 预测长期接触1，4-DX通过破坏氧化还原导致肝脏肿瘤发生的新假说 动态平衡，从而加剧了遗传的不稳定性。这一拟议的1，4-DX行动模式将是 在评估可能利用或调节的共生污染物的致癌效应方面的相关性 重叠的分子路径。我们建议(1)描述关键的氧化还原途径对1，4-DX的贡献 利用转基因氧化还原小鼠模型体内致癌作用，(2)确定 预测1，4-DX诱发的肝癌及其网络扰动的剂量反应模式 体内，以及(3)阐明共生污染物(TCE和1，1-DCA)修饰1，4-DX的能力 人肝细胞和斑马鱼模型系统的致癌性。

PROJECT SUMMARY 1,4-Dioxane (1,4-DX) is an emerging drinking water contaminant. The potential for 1,4-DX exposure is elevated for people living near Superfund or other types of 1,4-DX release sites. The International Agency for Research on Cancer has classified 1,4-DX as a group 2B carcinogen with the primary organ target being the liver in animal studies. Despite this concern, safety standards for 1,4-DX in drinking water have been slow to develop and vary widely, with the variability being related to the uncertainty associated with its liver carcinogenic potential. Mechanistic studies are urgently needed to (i) understand how 1,4-DX may contribute to liver carcinogenesis by itself or in combination with other co-occurring drinking water contaminants [such as trichloroethylene (TCE) and 1,1-dichloroethane (1,1-DCA)], (ii) determine the exposure concentration range over which these effects occur, and (iii) identify potentially more vulnerable subgroups. Our preliminary studies in mice have revealed molecular targets and pathways potentially involved in 1,4-DX carcinogenicity and set the stage for the proposed studies. These preliminary studies utilized various 1,4-DX concentrations (50, 500 and 5,000 ppm) in drinking water for periods of up to 3 month. These studies revealed mild liver cytotoxicity that is consistent with previous studies. The highest 1,4-DX dose induced assorted molecular changes in the liver including: (i) persistent induction of NRF2 and its target proteins involved in anti-oxidative response (i.e., GCLC, GCLM, HMOX1 and NQO1), (ii) time-dependent induction of CYP2E1 (key oxidative pathway capable of activating endogenous and xenobiotic compounds and a generator of reactive oxygen species), (iii) centrilobular accumulation of the lipid peroxidation by-product 4-HNE, and (iv) elevations in the DNA damage marker γH2AX. Importantly, these 1,4-DX-elicited molecular changes were amplified in a mouse model of systemic glutathione (GSH) deficiency. This project will build upon these intriguing findings and investigate our novel hypothesis predicting that long-term exposure to 1,4-DX causes liver tumorigenesis by disrupting redox homeostasis, thereby potentiating genetic instability. This proposed 1,4-DX mode of action would be of high relevance in assessing carcinogenic effects of co-occurring contaminants that may utilize or modulate overlapping molecular pathways. We propose to (1) delineate the contribution of key redox pathways to 1,4-DX liver carcinogenicity in vivo using transgenic redox mouse models, (2) identify the biological network motifs that predict 1,4-DX-induced liver carcinogenesis and the dose response pattern for perturbation of these networks in vivo, and (3) elucidate the capacity of co-occurring contaminants (TCE and 1,1-DCA) to modify 1,4-DX carcinogenicity in human hepatocyte cells and zebrafish model systems.